The present invention relates to a developing unit incorporated in an electrophotographic image forming apparatus and, more particularly, to a device for supplying a toner to the developing unit.
An electrophotographic copier, facsimile machine, laser beam printer or similar electrophotographic image forming apparatus has a developing unit which is operable with a one-component or a two-component developer. The developer is fed from the developing unit for developing a latent image electrostatically formed on a photoconductive element and representative of a document image. The one-component developer is constituted by a magnetic toner and lacks a carrier, while the two-component developer is made up of a non-magnetic or weakly magnetic toner and a magnetic carrier. The two-component developer is used more frequently than the one-component developer since it promotes easy control over the frictional charging of the toner and has high developability. In any case, the toner is sequentially consumed by the developing unit for development. It is, therefore, necessary to supply a fresh toner smoothly from a toner supply device to the developing unit. The toner supply device is in turn supplied with the toner from a toner cartridge.
A current trend in the image forming art is toward a large size, high speed apparatus. Since such an apparatus consumes a greater amount of toner, or developer, than conventional ones, the developing unit, toner supply device and toner cartridge themselves are increasing in size.
The problem with the toner is that it in nature is apt to form masses due to moisture. Therefore, when a great amount of toner is contained in a large toner cartridge, it is likely that the toner forms large masses in the cartridge or, in some storage conditions, it is locally concentrated in the cartridge and sets there. Should the toner in such a condition be fed from the toner cartridge to the toner supply device, the masses or the local concentration would be directly transferred to the toner supply device to prevent the toner from being fed smoothly from the toner supply device to the developing unit. This would lead to an irregular image density distribution on reproductions. Further, when the toner forms unusually large masses in the toner cartridge, it prevents a closer member or shutter of the cartridge from being returned from an open position to a closed position.